Energetics of Avian Growth: The Causal Link with BMR and Metabolic Scope

Abstract

Our point of departure is Lack’s (1968) viewpoint that avian growth rate is one of the parameters adjusted in the course of evolution to help match the needs of the brood to the foraging ability of the parents in nidicolous species. A second selective pressure, valid especially for nidifugous species, is to minimize the period of heightened predation risk when the chicks are small and cannot yet fly. Furthermore, Lack reasoned that the seasonal timing of growth required synchrony, between the period of maximal demand of the growing young and the period of greatest food abundance. A further selective pressure for rapid growth rate might be expected in strongly seasonal environments where it is imperative to complete development before the onset of unfavourable conditions. These considerations are based on the premise that changes in growth rate bring about large changes in the daily ration required to raise the chick, i. e. the energetic consequences of alteration of growth rate loom large in the daily energy budget.